Wireless communications technology today requires cellular radiotelephone products that have the capability of operating in multiple frequency bands. The normal operating frequency bands, in the United States for example, are analog, Code Division Multiple Access (CDMA) or Time Division Multiple Access (TDMA) or Global System for Mobile Communications (GSM) at 800 MHz, Global Positioning System (GPS) at 1500 MHz, Personal Communication System (PCS) at 1900 MHz and Bluetooth™ at 2400 MHz. Whereas in Europe, the normal operating frequency bands are Global System for Mobile Communications (GSM) at 900 MHz, GPS at 1500 MHz, Digital Communication System (DCS) at 1800 MHz and Bluetooth™ at 2400 MHz. The capability to operate on these multiple frequency bands requires an antenna structure able to cover at least these frequencies.
External antenna structures, such as retractable and fixed “stubby” antennas (comprising one or multiple coils and/or straight radiating elements) have been used with multiple antenna elements to cover the frequency bands of interest. However, these antennas, by their very nature of extending outside of the radiotelephone and of having a fragile construction, are prone to damage and may be aesthetically unpleasant. As the size of radiotelephones shrink, users are more likely to place the phone in pockets or purses where they are subject to jostling and flexing forces that can damage the antenna. Moreover, retractable antennas are less efficient in some frequency bands when retracted, and users are not likely to always extend the antenna in use since this requires extra effort. Further, marketing studies also reveal that users today prefer internal antennas to external antennas.
The trend is for radiotelephones to incorporate fixed antennas contained internally within the radiotelephone. At the same time, antenna bandwidth and efficiency are fundamentally limited by its electrical size. One known approach to overcome this problem is to use matching networks to match the antenna and source impedances over a specific frequency band. However, if the antenna is narrowband (because of its small size) to begin with, there is only limited increase in bandwidth that can be achieved before serious degradation of the radiated efficiency occurs. Therefore, there is a need for a small size and low cost internal antenna apparatus with multi-band frequency radiation capability. It would also be of benefit to provide this antenna apparatus driven by a single excitation port.
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